Re: flying with rifles
The TSA rule states that "Parts of Guns and Firearms" may NOT be carried on. Like RJW said, it is up to the geniuses at TSA what constitutes a "part of guns and firearms," but you need to check with them to confirm. I have, in the past, carried scopes on in my camera bag, but YMMV.
With the ever-changing regs/rules surrouding airport security and screening, who the hell knows what the TSA folks consider prohibited as a carry-on item. When you do check with them, be sure to ask if there is anything in writing that they can point you to that specifically allows/disallows what you are trying to do because even if someone tells you it is okay, you may be shocked when someone at the screening checkpoint tells you the opposite.